The present invention relates generally to voltage regulating apparatus. More particularly, the present invention relates to shell-type voltage regulating transformers of the type using saturating reactors to achieve voltage regulation.
Voltage regulating transformers are commonly used to supply a substantially constant voltage to a load over a relatively wide range of input voltage variations. Frequently, such transformers employ the expedient of a saturating reactor to facilitate the voltage regulating function. Conventionally, the saturating-transformer voltage regulator comprises a magnetic core including a primary winding connected to a suitable supply of unregulated input voltage and a pair of secondary windings connected in series opposing relationship across the load. Sometimes, one of the secondary windings is eliminated by connecting the primary winding in an autotransformer configuration. Examples of such devices are disclosed in U.S. Pat. Nos. 2,143,745 and 2,212,198 to Sola and in a July, 1937 article in Electronics Magazine, pages 14-16, entitled "Voltage Regulators Using Magnetic Saturation".
In the prior art saturating reactor transformers, the magnetic core is normally structured having a saturating core section and a high reluctance non-saturating section. The saturating core section may, for example, comprise a core section of narrowed cross-sectional dimension or, alternatively, saturation may be facilitated through the use of a resonant circuit as taught in the foregoing Sola patents. An air-gap is frequently provided in the non-saturating core section to increase its reluctance. In any event, as the input voltage supplied to the primary winding rises from zero, most of the resulting flux is coupled through the saturating core section due to its relatively low reluctance and transformed by one of the secondary windings into a voltage for application to the load. When the input voltage increases to a level sufficient to saturate the core section, the flux divides more equally between the saturating and non-saturating core sections due to the effective increase in reluctance of the saturated core section. While saturated, the core section operates above the knee of the magnetization curve thereby opposing any further increase in flux. Consequently, a large change in primary voltage produces a relatively small variation in the secondary voltage. The remaining secondary winding may be coupled to the non-saturating core section and connected in series opposing relationship with the first secondary winding for transforming the flux in the non-saturating core section into a voltage further reducing the total amount of output voltage variation.
While voltage regulating transformers of the foregoing type exhibit numerous desirable features, e.g. rapid response, simplicity and lack of adjustments and self-protection against overloads, they are also characterized by certain design deficiencies. In particular, the presence of a highly saturated magnetic core in the regulator produces a considerable stray magnetic field with a high harmonic content. These stray magnetic fields may severely interfere with the operation of the equipment with which the regulator is used and in fact, may mitigate against the use of the regulator at all. Furthermore, while the regulator may theoretically be shielded to reduce the deleterious effect of the stray magnetic field, prior art attempts in this regard have generally proven impracticable on the basis of cost and complexity considerations.